Preliminary Report: Syntax and Formal Semantics of Hybrid Chi

The hybrid χ (Chi) formalism integrates concepts from the dynamics and control theory with concepts from computer science. It also integrates a high expressivity with an elegant straightforward semantics, which is formally specified using a structured operational semantics. User-friendly modeling extensions are defined by means of a small straightforward syntactic translation. The χ language has a relatively large number of operators for discrete-event modeling, but it also allows specification of general differential algebraic equations, such as higher index systems. Its process instantiation mechanism enables encapsulation, hierarchical composition and reuse of processes. Modular composition is supported by means of parallel composition, and by means of different interaction mechanisms: handshake synchronization and synchronous communication for discrete-event processes, and shared variables for continuous-time processes. The syntax and semantics are illustrated using many different examples.